Four Kent State students died, and nine were hurt in the shootings, which contributed to the change in the public’s attitude toward the war.

Standoff: A number of National Guardsmen opened fire on the crowd of unarmed student protesters

Mr Canfora, who now directs the Kent May 4 Center, said the government’s decision is disappointing but not surprising.

‘I request your further independent investigation utilizing more objective analysis of this crucial digital, forensic evidence,’ he wrote to the Attorney general’s office.

The events of that chaotic day in Kent, Ohio, are still not fully understood, and interest in the case was reignited recently because of a recently enhanced audio recording.

A 2010 analysis of the recording concluded that someone may have ordered National Guard troops to prepare to fire on students during the campus protest.

That didn’t convince Mr Perez, however, writing to Mr Canfora that a government review was inconclusive in determining whether the recording provided such evidence.

The original reel-to-reel audio recording was made by Terry Strubbe, a student who placed a microphone in a window sill of his dormitory that overlooked the anti-war rally.

Fatalities: Four students were shot and killed while nine others were injured by bullets, including one who was left paralyzed

Mr Canfora found a copy of the audio tape in a library archive in 2007.

The recording was enhanced and evaluated by Plainfield, New Jersey-based audio experts Stuart Allen and Tom Owen at the request of The Plain Dealer in Cleveland. Both concluded that they hear someone shout, ‘Guard!’ Seconds later, a voice yells, ‘All right, prepare to fire!’

This is particularly interesting because of the conflicting reports of whether or not there was a specific order for the guards to open fire.

On the issue of a command to fire, Mr Perez said the government’s analyst showed ‘no military-like voice commands to fire or otherwise were heard; rather, many of the words heard were probably uttered by several different individuals located closer to the microphone.’

Anguish: The shooting prompted outcry across the country

In 1974, eight guardsmen tried on federal civil rights charges were acquitted by a judge.

‘Get down!’ someone shouts, presumably in the crowd.

A voice then says, ‘Guard! …’ followed two seconds later by a booming volley of gunshots.

Mr Allen removed extraneous noises – wind blowing across the microphone, for example – that obscured voices on the recording.

Allen’s review also had uncovered four ‘thuds’ more than a minute before the guardsmen opened fire, which he believed could have been the sound of a revolver firing.

In the letter, Mr Perez said the sounds were likely Strubbe’s door opening and closing. That conclusion is consistent with voices inside Strubbe’s room, Mr Perez said.

Four Kent State students died, and nine were hurt in the shootings, which contributed to the change in the public’s attitude toward the war.

Standoff: A number of National Guardsmen opened fire on the crowd of unarmed student protesters

Mr Canfora, who now directs the Kent May 4 Center, said the government’s decision is disappointing but not surprising.

‘I request your further independent investigation utilizing more objective analysis of this crucial digital, forensic evidence,’ he wrote to the Attorney general’s office.

The events of that chaotic day in Kent, Ohio, are still not fully understood, and interest in the case was reignited recently because of a recently enhanced audio recording.

A 2010 analysis of the recording concluded that someone may have ordered National Guard troops to prepare to fire on students during the campus protest.

That didn’t convince Mr Perez, however, writing to Mr Canfora that a government review was inconclusive in determining whether the recording provided such evidence.

The original reel-to-reel audio recording was made by Terry Strubbe, a student who placed a microphone in a window sill of his dormitory that overlooked the anti-war rally.

Fatalities: Four students were shot and killed while nine others were injured by bullets, including one who was left paralyzed

Mr Canfora found a copy of the audio tape in a library archive in 2007.

The recording was enhanced and evaluated by Plainfield, New Jersey-based audio experts Stuart Allen and Tom Owen at the request of The Plain Dealer in Cleveland. Both concluded that they hear someone shout, ‘Guard!’ Seconds later, a voice yells, ‘All right, prepare to fire!’

This is particularly interesting because of the conflicting reports of whether or not there was a specific order for the guards to open fire.

On the issue of a command to fire, Mr Perez said the government’s analyst showed ‘no military-like voice commands to fire or otherwise were heard; rather, many of the words heard were probably uttered by several different individuals located closer to the microphone.’

Anguish: The shooting prompted outcry across the country

In 1974, eight guardsmen tried on federal civil rights charges were acquitted by a judge.

‘Get down!’ someone shouts, presumably in the crowd.

A voice then says, ‘Guard! …’ followed two seconds later by a booming volley of gunshots.

Mr Allen removed extraneous noises – wind blowing across the microphone, for example – that obscured voices on the recording.

Allen’s review also had uncovered four ‘thuds’ more than a minute before the guardsmen opened fire, which he believed could have been the sound of a revolver firing.

In the letter, Mr Perez said the sounds were likely Strubbe’s door opening and closing. That conclusion is consistent with voices inside Strubbe’s room, Mr Perez said.